[1000mp] HEATHKIT SB-200 vs YAESU MUSEN FL-2100B

[Mike Schatzberg]

Thank you Tom.....nicely done....

73,

Mike Schatzberg
WB2AJI
----- Original Message ----- 
From: "Tom Rauch" <w8ji@akorn.net>
To: <1000mp@mailman.qth.net>
Sent: Tuesday, February 19, 2002 9:12 PM
Subject: Re: [1000mp] HEATHKIT SB-200 vs YAESU MUSEN FL-2100B


> > You folks at Heath most certainly built what has become an Amateur
> 
> I worked as an outside contractor doing designs. We were actually 
> in the process of developing several new products including a pair 
> of 3-500Z's with big components (to be called the Warrior II) when 
> the plug was pulled due to slumping kit sales.  
> 
> > Radio Classic, in the SB-200...rugged, reliable, stable, and most of
> > all, the best performance per dollar available....I built mine, more
> > or less around 1968, and have logged thousands of on the air hours.
> 
> Actually the 200 is one of the least stable amps, because 572B's 
> have long thin grid leads that make it difficult to effectively ground 
> the grids. Under some conditions you could make it take off, but 
> with normal loads on the amp it was fine.
> 
> The problem is for some odd reason all problems are blamed on 
> stability.
> 
> > have only changed my Cetron 572B's once, in all these years, and that
> 
> Cetron tubes were well built and tested properly, unlike recent 
> tubes. Good tubes are getting harder and harder to find as the 
> engineers all die off or retire, or manufacturing moves where QC or 
> experience is poor.
> 
> > was preventive maintenance...naturally, I always minimize the grid
> > current, by advancing the loading as much as possible, while tuning
> > for maximum power output, and never exceeding 500 mils keyed down
> > current on the grids...
> 
> Ouch. That is very high, and beyond the dissipation limit of the grid 
> by a large margin. But thoriated tungsten filament tubes are very 
> forgiving of grid overloads because of the materials used.  
> 
> > Regarding your comments on the bigger brother, which offers about 3 db
> > improvement in output over the SB-200,  you may recall from previous
> > communications, that my SB-220 has Chinese Pride tubes, which had
> > operated with great instability and lack of efficiency...and yes, your
> > postulation that poor vacuum may indeed be the culprit here, is
> > certainly a reasonable explanation...once the tube is sealed however,
> > how does one determine whether it's vacuum was pulled down
> > sufficiently?....
> 
> Only by high-voltage breakdown tests. The slightest amount of gas 
> greatly decreases voltage breakdown. The elements inside a tube 
> tube can outgass, in particular graphite anodes. Tubes must be 
> tested both before and after sustained operation. 
> 
> Tungsten filament power tubes normally have the gettering agent 
> on the anode, and the elevated temperature of operation activates 
> the getter. An arc can also getter the tube by breaking down 
> gasses. The trick is gettering the tube without going broke 
> replacing all the little parts that go boom when the anode current 
> reaches hundreds of amperes as the filter caps discharge to the 
> chassis through the grid of the tube.
> 
> Somehow people equate arcing to oscillations or instability, I sure 
> don't know why!
> 
> > what occurred...I only can say for now, that after the changes were
> > completed, all my issues disappeared suddenly...and the amplifier
> > operates with both efficiency and stability...This may be due to the
> > "gettering" of all remaining atmosphere within the envelope,
> 
> Yep, if you arc em often enough or if you ever manage to get the 
> anodes near red-hot for a long time you'll degass the tubes.
> 
> When manufactured, tubes are operated with the anodes glowing 
> cherry red for hours at extra filament voltage and allowed to arc, as 
> well as cycled through temperatures because gettering agents 
> liberate gasses at some temperatures and absorb the same 
> gasses at other temperatures. They also have to "cook" all the 
> trapped air out of the materials inside the tube.
> 
> The main problem with the Chinese and glass Russian tubes is 
> they never cooked em properly or tested them right, and the 
> materials are sometimes poor. When you get a good one it might 
> be OK, and some factories might be OK. The factories I've dealt 
> with were not, however.
> 
> Metal-ceramic tubes are a different story. They getter by cathode 
> or filament heat, and are sealed much better. You can sometimes 
> degas them just by running the filaments for several hours. 3-
> 500Z's actually have to be operated, and the anodes heated to a 
> slight color to degas.
> 
> If you don't heat the anodes up, 3-500's (and 572's) will eventually 
> go bad. And then when you least expect it, bang.
> 73, Tom W8JI
> W8JI@contesting.com 
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